1. Field of the Invention
The present invention relates generally to video tape recorders and more particularly to time signal encoding/decoding apparatus therefor.
2. Description of the Prior Art
Heretofore, numerous encoding/decoding devices have been employed to record a time and/or control signal onto a dedicated track of a video tape. Such recording is highly advantageous as it permits the tapes so recorded to be processed by automatic tape handling equipment for such purposes as cuing the tape, locating scenes recorded on the tape, editing the tape and synchronizing two tapes.
A popular format for time signal recording is the 80-bit code, commonly referred to as the SMPTE edit code, which is recorded with each frame of the video signal. In this code, the 80 bits which are assigned to the time code include bits 0 through 3, and 8 and 9 for encoding the current frame number; and bits 16 through 19, and 24 through 26 for encoding the seconds; bits 32 through 35, and 40 through 42 for encoding the minutes; and bits 48 through 51, and 56 through 59 for encoding the hours of the time. Bits 64 through 79 are used for encoding a synchronizing word.
The 80 bits of the code are recorded onto a dedicated track of the tape once each frame; in other words, at a rate of 2400 bits per second, using the bi-phase technique (where a zero is represented by a single phase reversal and a one by two phase reversals per bit period).
The SMPTE code is disadvantageous in that it requires the use of a dedicated track of the tape which could otherwise be utilized for other purposes.
Furthermore, the code requires the use of relatively wide band circuitry to process 2400 bits per second. As a consequence, before the coded signal may be reliably reproduced, the tape must be brought up to speed. Also, the code is highly susceptable to dropouts which occur when the tape comes off the head.
Additionally, to generate and to record the code requires relatively complex, expensive and unreliable equipment.